The present invention relates generally to imaging and, more particularly, to motion estimation of an object to be imaged.
Exemplary imaging systems comprise computed tomography (CT) imaging systems and magnetic resonance (MR) systems. In a CT imaging system, exemplary geometries comprise fan-beam geometry and cone-beam geometry. Typically, in CT imaging systems, an x-ray source emits a fan-shaped beam toward a subject or object, such as a patient or a piece of luggage. Hereinafter, the terms “subject” and “object” shall include anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately produces an image.
Generally, the x-ray source and the detector array are rotated about the gantry opening within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal point. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom.
Typically, each scintillator of a scintillator array converts x-rays to light energy. Each scintillator discharges light energy to a photodiode adjacent thereto. Each photodiode detects the light energy and generates a corresponding electrical signal. The outputs of the photodiodes are then transmitted to the data processing system for image reconstruction.
In head perfusion CT, the organ-of-interest is scanned in a cine mode (table remains stationary) while the contrast medium is injected into the patient and propagates in the blood circulation. From a sequence of reconstructed images, parameters such as the mean transit time (MTT), cerebral blood flow (CBF), and cerebral blood volume (CBV) can be calculated. These parameters can be used to differentiate viable versus nonviable tissues, and provide guidance to clinicians. To monitor the entire perfusion process, a patient is continuously scanned at a one second scan cycle for about fifty seconds. The rise and fall of the contrast medium is monitored within the blood vessels and all the other surrounding tissue. Based on the theses continuously scanned images, perfusion maps are calculated to show the distribution of several key physiological parameters for the brain.
A patient having a head CT may be unable to hold the head still and steady during the CT scanning. The movement of the head may result from the patient being young, old, severely injured, or other reasons. Head motion of the patient occurs more often in head perfusion CT. During the relatively long period of continuous scanning, head motion is often unavoidable and causes error in the generated perfusion map. Head motion in a perfusion study not only results in motion artifacts for individual images but also cause mis-registration of the group of images.
It is inconvenient for the patient to be asked to repeat the whole scanning process because of head motion during a short time. Therefore, it is desirable to develop a suitable approach so that the perfusion map can be formed even if the head motion exists.